Biosensing instruments used for the detection of analyte levels in blood (such as glucose and cholesterol) often employ disposable sample strips that include a well or reaction zone for receiving a blood sample. A microprocessor/read only memory (ROM) combination controls the operation of the biosensing instrument and enables it to execute various procedures to obtain a desired analyte reading. However, if the algorithm/procedure used to determine the analyte level is improved, supplanted, or otherwise changed, and it is desired to update the meter to employ the improved procedure, a redesign of the meter is generally the result. In addition, meters previously sold to customers are obsoleted--even though the improved procedure may merely require the substitution of one memory chip for another memory chip.
Prior art biosensing meters have employed both current sensing and reflectance techniques for detection of analyte levels in blood samples. In reflectance-type meters, variations in sample strip test chemistries were accommodated through the provision of a removable memory chip that carried information regarding a specific batch of sample strips. In U.S. Pat. No. 5,053,199 to Keiser et al. and assigned to the same assignee as this application, a biosensing meter of the reflectance type is provided with a pluggable, programmable ROM that contained information pertinent to the optical characteristics of a particular batch of sample strip test chemistries. Such information enables the user to obtain an analyte reading without being required to mechanically insert calibration information (that had been previously provided with different packages of sample strips). That calibration information includes a table or set of tables that convert a reading obtained from an optical sensor to an analyte concentration value. Keiser et al. enables such calibration information to be directly loaded from the ROM to the meter.
In U.S. Pat. No. 4,975,647 to Downer et al., an analytical machine (e.g., a chromatograph) that employs consumable fluids is provided with a facility to receive a pluggable memory module. That memory module contains information concerning the timing of calibration operations, information identifying the fluids container, information identifying a class of analyzers with which the fluids container is usable, and information identifying the concentration of the fluids. Such information is then used to manage the frequency and times at which the instrument is calibrated and to further assure that a fluid pack is mated with an instrument that can properly utilize the fluids. In one example, Downer et al. describe a blood analyzer with a pluggable memory module that identifies the type of blood analyzer with which the fluid pack is intended to be used; the manufacturing lot of the fluid pack; a serial number uniquely identifying the fluid pack; concentrations of an electrolyte solution in the fluid pack; calibration zone times; "slippage" variables and a conventional two byte cyclic redundancy check (CRC) word.
The prior art includes further disclosures of biosensing instruments that employ disposable sample strips. In U.S. Pat. No. 5,108,564 to Szuminsky et al., a biosensing instrument is disclosed that measures glucose concentrations in blood. The instrument depends upon a reaction wherein glucose, in the presence of an enzyme, catalyzes a reaction of potassium ferricyanide to potassium ferrocyanide. After the reaction has completed, a voltage is applied across a reaction zone and causes a reversal of the reaction with an accompanying generation of a small, but measurable current. That current is termed the Cottrell current and, in dependence upon the concentration of glucose in the reaction zone, follows a predetermined curve during the reverse reaction. A reading of the Cottrell current is converted into an indication of glucose concentration. The instrument also senses an impedance across the reaction zone and determines when a blood sample has been emplaced therein by detecting a sudden change in current flow. At such time, an incubation period is commenced, followed by application of a potential across the reaction zone and measurement of the Cottrell current.
European Patent Application 0 471 986 A2 of Tsutsumi et al. discloses a blood glucose measurement system that employs disposable sample strips. The Tsutsumi et al. system detects the presence of a blood sample by sensing a resistance across a pair of electrodes. It further employs a plurality of sample-like strips, each having a specific resistance value which distinguishes it from other strips. Each of those strips has a particular application, i.e., for use during an adjustment mode of the instrument, during an error compensation mode, during a calibration mode, etc.
U.S. Pat. No. 4,999,582 to Parks et al., assigned to the same Assignee as this application, describes a biosensor electrode excitation circuit for determining if a sample strip has been properly inserted into a meter and if at least one electrode on the sample strip exhibits a proper level of contact resistance.
U.S. patent application Ser. No. 07/451,309, filed Dec. 15, 1989, to White, entitled "Biosensing Instrument and Method" and assigned to the same assignee as this application, teaches a biosensing instrument which employs the "Cottrell" curve relationship to determine glucose concentrations. In that instrument, current flow is proportional to the concentration of an analyte in the test cell; however, when something is amiss in the test cell, the current that results may bear no relationship whatever to analyte concentration. White indicates that a relationship exists that enables a determination to be made whether current flow through a reaction zone is, in fact, following the Cottrell relationship. More specifically, the ratio of the square roots of succeeding sample times, for all analyte concentration curves, to inversely approximate the ratio of the measured Cottrell currents at those same sample times. If over succeeding time periods, the ratios are equal (within limits), the measurement system is properly following the Cottrell relationship. If the ratios found are not equal, the measurement is disregarded.
U.S. Pat. No. 4,940,945 to Littlejohn et al. describes an interface circuit for use in a biochemical sensing instrument. A disposable cartridge is employed that includes a pair of electrodes across which resistance measurements are taken. Circuitry is disclosed for sensing the presence of a fluid sample by an initial resistance measurement, and also the level of fluid in the cartridge.
U.S. Pat. No. 4,420,564 to Tsuji et al. describes a blood sugar analyzer that employs a reaction cell having a fixed enzyme membrane sensor and a measuring electrode. The Tsuji et al. system includes several fail/safe procedures, one to determine that the reaction is taking place within specifically defined temperature limits and a second to determine that the reaction current remains within a predetermined range.
While the above prior art indicates that it is known to employ pluggable read only memories for insertion of data regarding characteristics of disposable sample strips (and/or fluid packs), none addresses the problem of enabling a biosensing meter to adapt to substantially revised test protocols and procedures without the need for redesign of the electronics or meter.
Accordingly, it is an object of this invention to provide a biosensing meter with a pluggable memory module that enables substantial reconfiguration of test procedures and parameters employed by the meter.
It is another object of this invention to provide a biosensing meter with a pluggable memory module that enables threshold potentials, test times, delay periods and other pertinent test procedures and constants to be inserted and/or altered.
It is yet another object of this invention to provide a biosensing meter with a pluggable read only memory wherein data read from the read only memory at sequential times during the use of the meter enables a determination to be made as to whether the read only memory has been switched during a test procedure.